The epikarst, which consists of highly weathered rock in the upper vadose zone of exposed karst systems, plays a critical role in determining the hydrologic and geochemical characteristics of recharge to an underlying karst aquifer. This study utilized time series (2007–2014) of hydrologic and geochemical data of drip water collected within James Cave, Virginia, to examine the influence of epikarst on the quantity and quality of recharge in a mature, doline-dominated karst terrain. Results show a strong seasonality of both hydrology and geochemistry of recharge, which has implications for management of karst aquifers in temperate climatic zones. First, recharge (discharge from the epikarst to the underlying aquifer) reaches a maximum between late winter and early spring, with the onset of the recharge season ranging from as early as December to as late as March during the study period. The timing and duration of the recharge season were found to be a function of precipitation in excess of evapotranspiration on a seasonal time scale. Secondly, seasonally variable residence times for water in the epikarst influence rock-water interaction and, hence, the geochemical characteristics of recharge. Overall, results highlight the strong and complex influence that the epikarst has on karst recharge, which requires long-term and high-resolution data sets to accurately understand and quantify.

Development of the coastal aquifer systems of Southern California has resulted in overdraft, changes in streamflow, seawater intrusion, land subsidence, increased vertical flow between aquifers, and a redirection of regional flow toward pumping centers. These water-management challenges can be more effectively addressed by incorporating new understanding of the geologic, hydrologic, and geochemical setting of these aquifers. Groundwater and surface-water flow are controlled, in part, by the geologic setting. The physiographic province and related tectonic fabric control the relation between the direction of geomorphic features and the flow of water. Geologic structures such as faults and folding also control the direction of flow and connectivity of groundwater flow. The layering of sediments and their structural association can also influence pathways of groundwater flow and seawater intrusion. Submarine canyons control the shortest potential flow paths that can result in seawater intrusion. The location and extent of offshore outcrops can also affect the flow of groundwater and the potential for seawater intrusion and land subsidence in coastal aquifer systems. As coastal aquifer systems are developed, the source and movement of ground-water and surface-water resources change. In particular, groundwater flow is affected by the relative contributions of different types of inflows and outflows, such as pump-age from multi-aquifer wells within basal or upper coarse-grained units, streamflow infiltration, and artificial recharge. These natural and anthropogenic inflows and outflows represent the supply and demand components of the water budgets of ground-water within coastal watersheds. They are all significantly controlled by climate variability related to major climate cycles, such as the El Niño–Southern Oscillation and the Pacific Decadal Oscillation. The combination of natural forcings and anthropogenic stresses redirects the flow of groundwater and either mitigates or exacerbates the potential adverse effects of resource development, such as declining water levels, sea-water intrusion, land subsidence, and mixing of different waters. Streamflow also has been affected by development of coastal aquifer systems and related conjunctive use. Saline water is the largest water-quality problem in Southern California coastal aquifer systems. Seawater intrusion is a significant source of saline water, but saline water is also known to come from other sources and processes. Seawater intrusion is typically restricted to the coarse-grained units at the base of fining-upward sequences of terrestrial deposits, and at the top of coarsening upward sequences of marine deposits. This results in layered and narrow intrusion fronts. Maintaining the sustainability of Southern California coastal aquifers requires joint management of surface water and groundwater (conjunctive use). This requires new data collection and analyses (including research drilling, modern geohydrologic investigations, and development of detailed computer groundwater models that simulate the supply and demand components separately), implementation of new facilities (including spreading and injection facilities for artificial recharge), and establishment of new institutions and policies that help to sustain the water resources and better manage regional development.

Abstract The isotopic composition of water has been widely used to investigate groundwater dynamics and recharge processes. In the present study, we have analysed the isotopic composition of groundwater, and of Sutlej River, Yamuna River, Ghaggar River and canal water from the Sutlej-Yamuna plain in NW India. We document spatial and depth-related variations in δ 18 O and deuterium excess (d-excess) values of groundwater in three zones based on topography and slope (zones I–III) from NE to SW. In Zone I, precipitation is the main recharge source for groundwater, as indicated by the isotopic values. We infer mixed recharge from precipitation and irrigation return flow in Zone II. Zone III records depleted δ 18 O and higher d-excess values in most of the groundwater samples, suggesting active recharge from canals. Further, we have calculated the contribution of canal water in groundwater using the hydrograph separation approach and have also quantified the uncertainty in its estimation. We note significant spatial and depth-related variability in the canal water contribution to groundwater recharge. The canal contribution is as high as 83 ± 10% at 18 m below ground level (bgl) in Zone III, and as low as 5 ± 3% at 43 m bgl in Zone II. The present study provides the baseline data on recharge processes in NW India, which is critical for developing sustainable management strategies for groundwater resources in this region.

Abstract Urbanization is increasing worldwide, and it has drastic effects on groundwater systems with ramifications for water management. Effects can include overexploitation, subsidence, water quality deterioration, destruction of environmental resources, increased runoff, alteration of the permeability and porosity fields, and changes in recharge. Commonly, it is assumed that recharge decreases, but data indicate the opposite: Groundwater recharge increases because of leaky utility (water and sewage) systems and urban irrigation. Urban areas are hydrologically similar to karst settings because they possess internal drainage (storm sewers), surface streams (paved drainage ways) that flow after heavy rains, and a shallow permeability structure dominated by fractures, conduits, and caves (buried utility trenches, abandoned pipes, etc.) that evolves very quickly. Secondary porosity from underground construction is similar in magnitude to karst secondary porosity. These structures and utility trenches increase permeability and make prediction of groundwater flow and transport difficult. Recharge is grouped into the following categories: direct (from precipitation), indirect (from surface water bodies and leaky utility systems), localized (through preferential pathways such as sinkholes), and artificial. Indirect recharge is commonly ignored in urban water budgets, but water main losses range from 5% to over 60%. Additional recharge comes from leaky sewers, leakage from beneath homes and industries, and irrigation return flow (e.g., lawn overwatering). A case study of Austin, Texas, demonstrates significant indirect recharge and the difficulties in its estimation. Nearly 8% of Austin water main flow is lost to become recharge. However, lawn irrigation may be a larger source.

Abstract In India, demand for water has increased due to population growth and the competition induced by economic aspirations for developmental activities. Despite abundant rainfall, a few crucial issues for the water crisis are as follows: erratic rainfall and zonal disparity in the distribution of the available water and its inefficient use across different regions, unregulated groundwater extraction, worsening water quality, inefficient management and implementation of the regulations, lack of an ethical framework, and so on. Over 70% of the surface water is polluted and is unsafe for drinking/farming. More than 65% of irrigated agriculture and 80–85% of the rural and urban water supply and drinking water supply depend on groundwater. However, people have inadequate knowledge and awareness and different perceptions of this vital natural resource and how vulnerable it is. Geoscientists have a significant role to play to increase public awareness on the topic of ‘groundwater ethics’ and its interaction with people, their habits and the water in order to control indiscriminate water extraction and its wasteful utilization. To protect groundwater from depletion, emphasis should be placed on community-focused groundwater use, the price of water extraction and the costs and benefits of water allocation for irrigation needs where consumptive use is high compared to all other uses with relatively smaller water needs.